This invention relates to a detector with a capacitance sensor (or capacitive sensor) for detecting an object that may be caught or is likely to be caught by a closing slide door, say, of a vehicle.
Controller systems for a structure adapted to open and close such as an electrically powered slide door of a vehicle are provided with a safety feature for preventing an object such as a person's body from becoming caught thereby. In the case of an automatically closing mechanism adapted to automatically bring the structure (hereinafter referred to as the door) to the fully closed position even after the user stops its operation, this may be done by detecting an object that is caught or likely to be caught and at least stopping the operation of the automatically closing mechanism. The motion of the door may also be reversed.
Prior art detectors used for such a purpose were either for direct detection or for indirect detection. Indirect detection may be made on the basis of operation data of the driver motor such as its angular position and its rotary speed or the driving power. Direct detection may be made by means of a sensor for detecting a human body approaching or coming into contact with an open end portion of the door. Indirect detection has problems in that it is relatively difficult to quickly and reliably detect a caught object at a load as low as possible. Direct detection is superior from the point of view of reliability because an object of detection is directly detected but since a pressure-sensitive switch has been used as a sensor of this type, detection could not be made quickly at a low load. This was because a pressure-sensitive switch comprised a cable, say, of a conductive resin material adapted to function when deformed by a pressure from the target object such that an internal conductive member comes into a contacting position. In other words, the switch can function only after the target object comes into contact with a pressure of a certain magnitude and the function of preventing the object from being caught begins to work only at such point in time.
A sensor for generally detecting an approaching target object without contacting it may be of an optical type, an electromagnetic wave type or a capacitance type. Sensors of the optical type have the problem that the detection area cannot be defined along a curved end portion of a structure such as a door, that is, there result so-called insensitive zones. With a sensor of the electromagnetic type, it is difficult to limit the directionality to the direction of approach to the open end portion of the door and there is a high probability of an erroneous detection. Capacitance-type sensors seem to be superior because they can be easily attached to a curved end part, there is no insensitive part and the directionality can be easily controlled. The present inventors have been examining how to use a capacitance sensor as a detector for an object caught or being caught by a powered slide door, say, of a vehicle.
No prior art example is known to have shown the use of a capacitance sensor for detecting an object caught by a powered slide door of a vehicle. Japanese Patent Publication Tokkai 10-96368 has disclosed a detector using a capacitance sensor for a door of a railroad passenger car. Japanese Patent Publication Tokkai 2001-264448 has disclosed the use of a capacitance sensor for detecting a person caught by a shutter. Japanese Patent Publication Tokkai 2001-318162 has disclosed a pin ball machine sensor with a high sensitivity for detecting a passing pin ball by providing a plurality of pairs of capacitance-providing electrodes and on the basis of differentials of signals corresponding to each capacitance.
According to the studies by the present inventors, however, capacitance sensors as described above cannot be used for a structure such as a door because of the problems of the kinds to be described below if there are water drops such as rain drops.
(A) When the door is at a positive potential, the sensor is likely to function incorrectly, becoming switched on if a body part such as a hand of a person merely approaches the outer side surface of the door while water drops such as rain drops are attached to it.
(B) If water drops become attached to the detection surface of a capacitance sensor over its entire width, the sensor is likely to function incorrectly, becoming switched on because of these water drops. In the case of a sensor with a sectionally U-shaped shield electrode with an opening on the side of the detection surface in order to provide directionality as much as possible only on the side of the detection surface, for example, a detection signal is likely to be incorrectly switched on if water drops become attached so as to span between both its end positions.
(C) If water drops become attached continuously from the door to a portion of the detection surface, an error is likely to result although water drops may not be attached all over the detecting surface.
It is therefore an object of this invention to provide a capacitance sensor which is not likely to function incorrectly even in an environment where water drops such as rain drops fly around, as well as a reliable detector using such a sensor for detecting an object being caught by a door.